The importance of ingested soils in supplying fluorine and lead to sheep grazing contaminated pastures in the Peak District mining area of Derbyshire, UK.

For sheep grazing pastures in areas of mineralisation and former metalliferous mining activity, an excessive intake of potentially harmful elements (PHEs) such as fluorine (F) and lead (Pb) can result in clinical and subclinical toxicity. The prime aim of our work was to calculate the intakes of both of these PHEs by sheep grazing pastures in the mineralised/mined Peak District area of Derbyshire. The bi-monthly sampling of topsoils (0-15 cm depth) and the faeces of sheep from fields at seven farms was undertaken for a 1-year period. These samples were analysed for titanium that allowed the rates of soil ingestion (and hence also herbage ingestion since we assume that the sheep have an overall diet of 1 kg dry matter (DM)/day) to be determined. Our findings were then combined with previously published soil and soil-free pasture herbage F and Pb concentrations determined from the seven farms to calculate the intakes of both PHEs. The results show seasonal variations of soil ingestion at the seven farms ranging from <0.1 to 20.1 % of the DM intake (median=3 %), with the highest rates of ingestion being associated with the winter-spring (i.e. December-April) period. Our calculations show that at some farms, sheep can be exposed to dietary concentrations in excess of recommended guidelines potentially throughout the whole year, though livestock movement to less-contaminated pastures would lessen any toxic impact. Because the soil concentrations are greater than those associated with soil-free pasture herbage, ingested soils are the main dietary source of Pb and (especially) F to sheep. However, subjecting freshly sampled topsoils to sequential extraction procedures undertaken in the laboratory indicates that the majority of Pb and (especially) F may not be readily soluble in the ovine digestion system, so reducing the quantities of both PHEs available for absorption.

Human geophagia, calabash chalk and undongo: mineral element nutritional implications.

The prime aim of our work is to report and comment on the bioaccessible concentrations - i.e., the soluble content of chemical elements in the gastrointestinal environment that is available for absorption - of a number of essential mineral nutrients and potentially harmful elements (PHEs) associated with the deliberate ingestion of African geophagical materials, namely Calabash chalk and Undongo. The pseudo-total concentrations of 13 mineral nutrients/PHEs were quantified following a nitric-perchloric acid digestion of nine different Calabash chalk samples, and bioaccessible contents of eight of these chemical elements were determined in simulated saliva/gastric and intestinal solutions obtained via use of the Fed ORganic Estimation human Simulation Test (FOREhST) in vitro procedure. The Calabash chalk pseudo-total content of the chemical elements is often below what may be regarded as average for soils/shales, and no concentration is excessively high. The in vitro leachate solutions had concentrations that were often lower than those of the blanks used in our experimental procedure, indicative of effective adsorption: lead, a PHE about which concern has been previously raised in connection with the consumption of Calabash chalk, was one such chemical element where this was evident. However, some concentrations in the leachate solutions are suggestive that Calabash chalk can be a source of chemical elements to humans in bioaccessible form, although generally the materials appear to be only a modest supplier: this applies even to iron, a mineral nutrient that has often been linked to the benefits of geophagia in previous academic literature. Our investigations indicate that at the reported rates of ingestion, Calabash chalk on the whole is not an important source of mineral nutrients or PHEs to humans. Similarly, although Undongo contains elevated pseudo-total concentrations of chromium and nickel, this soil is not a significant source to humans for any of the bioaccessible elements investigated.

Soil ingestion by sheep grazing the metal enriched floodplain soils of mid-Wales.

Floodplain soils within and downstream from the mineralised and mined areas of mid-Wales, are contaminated by metals, especially Pb, because of historical and contemporary fluvial pollution. Rates of soil ingestion by sheep grazing these sites have been quantified to establish the relative importance of the soil-plant-animal and soil-animal pathway of metals. The highest rates of soil ingestion occurred during the winter/spring period. During March, soil ingestion exceeded 30% of the D.M. intake at 2 of the 11 sites investigated. The total daily intake of metals by sheep reflects the degree of soil metal enrichment, and is elevated during the winter/spring period, coincident with the higher rates of soil ingestion and the generally higher pasture herbage metal concentrations. Because the soil-plant transfer of Pb is low, ingested soil is often the major pathway of this metal to sheep. This is especially evident in March and May when on average 80.0 and 82.9%, respectively of the Pb intake was via soil ingestion. At one site in May, 97% of the Pb intake was attributable to ingested soil. Even when soil-plant transfers are not so low, as found for Cu and Zn, ingested soil can occasionally supply greater than 60% of these metals to the animal. However, despite the potential importance of soil ingestion, little is known about the availability to and absorption of soil-borne metals by animals.